Ultrasound is widely used for imaging a patient's internal structures without risk of exposure to potentially harmful radiation, as may occur when using X-rays for imaging. An ultrasound examination is a safe diagnostic procedure that uses high frequency sound waves to produce an image of the internal structures of a patient's body. Many studies have shown that these sound waves are harmless and may be used with complete safety, even to visualize the fetus in pregnant women, where the use of X-rays would be inappropriate. Furthermore, ultrasound examinations generally require less time than examinations using other imaging techniques, and ultrasound examinations are typically less expensive than examinations using other imaging techniques.
More recently, the use of high intensity focused ultrasound (HIFU) for therapeutic purposes, as opposed to imaging, has received significant attention in the medical community. HIFU therapy employs ultrasound transducers that are capable of delivering 1,000-10,000 W/cm2 to a focal spot, in contrast to diagnostic imaging ultrasound, where intensity levels are usually below 0.1 W/cm2. A portion of the energy from these high intensity sound waves is transferred to a targeted location as thermal energy. The amount of thermal energy thus transferred can be sufficiently intense to cauterize undesired tissue, or to cause necrosis of undesired tissue (by inducing a temperature rise greater than about 70° C.) without actual physical charring of the tissue. Tissue necrosis can also be achieved by mechanical action alone (i.e., by cavitation that results in mechanical disruption of the tissue structure). Further, if the vascular system supplying blood to an internal structure is targeted, HIFU can be used to induce hemostasis. The focal region of this energy transfer can be tightly controlled so as to obtain necrosis of abnormal or undesired tissue in a small target area without damaging adjoining normal tissue. Thus, deep-seated tumors can be destroyed with HIFU without surgical exposure of the tumor site.
An important consideration in any type of ultrasound therapy system is the form factor of the therapy head (i.e., the portion of the system containing the therapy transducer, which is generally positioned proximate the treatment site before providing therapy). The size and shape of the therapy head in which the therapy transducer is mounted varies depending upon the intended treatment site. For example, to facilitate placement of the therapy head within the corresponding body cavities, transrectal and vaginal therapy probes are each typically elongate in shape and narrow in size.
One significant application of therapeutic ultrasound is the use of HIFU for hemostasis applications. The application of HIFU in an intra-operative setting presents challenges due to the limited space available. It would be desirable to provide a therapy probe having a therapy head exhibiting a relatively small form factor. A significant challenge in providing such a design is that therapeutic transducers generally produce a considerable amount of heat, and cooling is required to prevent damage to surrounding tissue or to the therapy head itself. Therapy heads are often encapsulated in a latex balloon filled with water, and the water is circulated to provide the required cooling, as well as to facilitate acoustically coupling the therapy head to target tissue. Unfortunately, such balloons are bulky, and are not well suited to achieving a therapy head having a small form factor. It would thus be desirable to provide a therapy probe having a therapy head exhibiting a relatively small form factor, which can be cooled without requiring the use of a bulky balloon.